The need for vaccines to control malaria and other parasitic diseases remains unabated. For malaria, the need is particularly pressing as it continues to dominate vast subtropical and tropical areas of the world. An effective vaccine against this disease would contribute significantly to restrain it and dulling the sharp cutting edge of its repeated resurgence.
For lack of effective immunization procedures, malaria and other parasitic diseases continue for the most part to be treated after inception, with varying degrees of success. While numerous attempts have been made to isolate protective antigenic factors associated with these parasites, purification and recovery of antigens having a high immunizing efficiency in quantities suitable for large scale administration have not been effected for most infectious parasitic diseases.
Rodents and primates have been variously vaccinated against malaria with crude plasmodial fragments separated from host blood cells (see e.g., D""Antonio et al., Nature 223: 507-509 (1969) (Reference I); D""Antonio et al., Science 168: 1117-1118 (1970) (Reference II); D""Antonio et al. Exptl. Parasitology 31: 75-81 (1972) (Reference III), isolated membrane particles (see e.g., References II, III; D""Antonio et al. J. Am. Osteopathic Assoc. 73: 649-652 (1974) (Reference IV); Speer et al., J. Protozoal. 23: 437-442 (1976) (Reference V), and purified membrane subfractions (see e.g., D""Antonio in Immunological and Serological Aspects of Clinical Parasitology, W. Ball and V. Iralou, Eds. (Eastern Penn. Branch of the Am. Soc. of Microbiology, p. 59, 1981) (Reference VI). However, further purification of the involved protective antigen(s) has been hampered by the absence of effective non-denaturing techniques for separating them from their insoluble carrier components. For example, specific attempts to isolate malarial plasmodial protective antigens from associate plasmodial material with acetic acid (D""Antonio et al. Abs. of the Am. Soc. for Microbiol., Abstr. E68, 1980) or lithium 3,5-diiodosalicylate (Reference VI and D""Antonio et al., Abs. of the Am. Soc. for Microbiol., Abstr. E98, 1979) have not proved entirely successful. Thus, solubilization and recovery of such antigenic factors from these and related materials would open the way for their final purification and is the next crucial step in advancing the immunochemistry, immunobiology, and vaccine technology of malaria and related diseases.
Accordingly, the invention comprises a method for the solubilization and recovery of protective antigenic factors associated with protozoan parasites. The invention further comprises a method for the purification and recovery of protective antigens of protozoan parasites, particularly parasites of the genuses Plasmodium, Babesia, Trypanosoma, Leishmania, Trichomonas, Entamoeba, Toxoplasma, Pnemocystis, Aegyptianella, Theileria, Anaplasma, and most particularly intraerythrocytic protozoan parasites. The invention additionally provides a vaccine capable of conferring immunity against such parasites comprising the antigenic factors purified and recovered according to the invention. The invention further includes a method for conferring immunity against protozoan parasites comprising administering the parasite antigenic factors purified and recovered according to the invention to a mammal or other vertebrate in immunity-conferring doses. The invention particularly provides a method for the direct extraction of parasite antigenic factors from intact erythrocytes infected with malarial parasites of the genus Plasmodium, particularly P. berghei, P. malariae, P. vivax, P. knowlesi, P. ovale and P. falciparum, and a method for immunizing mammals or other vertebrates against infection by these parasites. Also, the invention provides a method for diagnosing infection by protozoan parasites. 
Broadly, the invention comprises a method for the solubilization and recovery of parasite protective antigenic factors associated with parasite material comprising dispersing the antigenic factors from intact or fractured cells or other tissues infected with protozoan parasites or from free parasite forms with a detergent, and separating the solubilized antigenic factors from the dispersing agent and cell or tissue residues; and products made by such method. The recovered antigenic factors are useful in vaccines for conferring specific immunity in mammals or other vertebrates to the infecting parasite, or as diagnostic agents.